Bull grew up in a housing complex in the New Mexican Shared Interest Zone, living with his father and Mexican mother, as well as many other family members. As a sixteen year old he went to Alamogordo and worked his two-year service stripping down ancient solar electricity stations to avoid going on basic, living in a dorm with ten other boys.
Despite being most qualified to lead the expedition to the Ring aboard Chief of Security due to the politics of him being from Earth and not from the Belt. Ashford was made captain instead. Michio Pa was made XO instead. Fred Johnson, despite respecting him and promoting Michio Pa, asked Bull to "make it work".
Once the Seung Un explodes and the apparent message from Jim Holden is broadcast, Bull is responsible for recommending to Ashford that the Behemoth summarily fire on the Rocinante as a statement that it denies and rejects any claim over the Ring in the name of the OPA as professed by the crew of Jim Holden's ship.
The Slow Zone Incident Edit
When the speed limit in the slow zone changed due to hostilities from Martians aboard Ring Station, Bull suffered a spinal fracture aboard the Behemoth, paralyzing him from the waist down. Sam gave him mechanical legs.
In a attempt to slow down or take out some of the approaching belters in Martian Power Armor. Carlos uses the remaining card like grenades from the Martians, to blow up a approaching belters in Power Armor. Carlos while successful, sacrifices himself in this action.
In one of the last conversations with Holden, Carlos predicts that the Medina Station will be his in the future but not yet.
In a conversation with Fred upon returning to Tycho Station after the trip to Ilus, Fred and Holden eulogize Carlos by saying he probably saved the entire Sol System, and he would think that's "pretty damn cool".